Thermal spray coatings are used in a wide variety of industrial applications. Such coatings are often of materials selected so as to provide high hardness and outstanding wear resistance to increase the life expectancy of materials that are coated. The use of thermal spray coatings often achieves a reduction in wear and a corresponding increase in part life. The improvement in the wear resistance as a result of the use of a thermal spray coating has also enabled the substitution of cheaper coating materials for fully alloyed parts.
Thermal spray coatings are often applied by a plasma spray gun. Where such coatings are applied to increase wear resistance, wear resistant materials such as tungsten carbide particles are mixed or alloyed with a binding agent. During the spray process, the tungsten carbide particles are exposed to temperatures in excess of 20,000.degree. F. During such thermal exposure, tungsten carbide in the presence of oxygen may be subject to decarburization. In such a reaction, a desirable WC phase is disassociated to form less desirable constituents such as W.sub.2 C, CO.sub.2, free tungsten and carbon. Although W.sub.2 C is harder than WC, in most applications W.sub.2 C is not a desirable phase due to its brittleness.
The extreme temperatures of a plasma spray gun may Promote or accelerate an adverse oxygen reaction in other constituents of thermal spray coatings as well. Examples of these materials include other carbides, diamonds and transition metal nitrides. The end result is a coating with less than optimal intended properties. Accordingly, a need has existed for a method of minimizing the decarburization or other forms of high temperature oxygen related reactions associated with plasma spray coating.